This application claims the benefit of Korean Patent Application No. 2001-2627 filed on Jan. 17, 2001, in the Korean Industrial Property Office, the disclosure of which is incorporated herein by reference.
1. Field of the Invention
The present invention relates to an optical switch, and more particularly, to an optical switch which can control a proceeding direction of an optical signal by heating liquid with the use of a laser heating unit so that the liquid can move into or out of the path of the optical signal.
2. Description of the Related Art
An optical switch is used to transmit a particular optical signal among many optical signals for various channels to a channel in a desired direction in an optical communications system, in particular, in an optical communications system adopting a wavelength division multiplexing method. In this type of optical communications system, waveguides cross perpendicular to each other, and a cell capable of containing liquid is provided at the cross point of the waveguides to be angled with respect to the waveguides. To perform a switching operation, there are methods of generating air bubbles in the liquid in the cell and moving the liquid in the cell by using a change in surface tension according to a difference in temperature at a boundary surface of air.
Referring to FIGS. 1 and 2, in a conventional optical switch, waveguides 103 are arranged in the form of an Nxc3x97M matrix on a substrate 100. A cell 110 containing liquid 105 is diagonally installed at a cross point 103a of the waveguides 103. A heater 115 that heats the liquid 105 is installed on the substrate 100 together with the waveguides 103. Here, the cell 110 includes a head portion 110a where the liquid 105 is contained and a tail portion 110b disposed at the cross point 103a. 
The operation of the optical switch having the above structure is described with reference to FIG. 2. First, when an optical signal is to be transmitted, the heater 115 heats the liquid 105. Then, the surface tension of a boundary surface between the liquid 105 and air decreases so that the liquid 105 moves toward the tail portion 110b of the cell 110. Since the optical switch is a micro device, a force mainly applied to the liquid 105 is not gravity but surface tension so that the surface tension greatly affects the movement of the liquid 105. Also, since the surface tension has the feature of being inversely proportional to a temperature and an electric field, when heat is applied to the liquid 105, the surface tension decreases and the liquid 105 moves in a direction in which the surface tension decreases.
When the liquid 105 moves toward the tail portion 110b of the cell 110, an optical signal passes through the liquid 105 and proceeds forward. Here, the liquid 105 having a refractive index the same as or similar to that of the waveguides 103 is used so that when the optical signal meets the liquid 105, the optical signal is hardly reflected and passes through the liquid 105.
To reflect the optical signal, heating by the heater 115 is stopped to increase the surface tension between the liquid 105 and air so that the liquid 105 moves toward the head portion 110a of the cell 110. When an optical signal is input after the liquid 105 completely moves toward the head portion 110a from the tail portion 110b, the optical signal is totally reflected by the cell 110. Here, since the gas inside the cell 110 has a refractive index less than that of the waveguides 103, an optical signal input at a predetermined angle or more can be total-reflected. For example, the liquid 105 of a cell (A) in row 3, column 2 and a cell (B) in row 2, column 3, is heated to move the liquid toward the tail portion 110b so that an optical signal passes through the two cells. At the same time, the liquid 105 in the remaining cells is not heated, and therefore the liquid stays at the head portion 110a of the cell 110 so that the optical signal is total-reflected and can be alternatively transmitted along a desired path. Thus, the optical signal input is directed toward a cell in row 3, column 1, as shown in FIG. 2, is total-reflected at this cross point, and passes through the cell (A) in row 3, column 2 and is then output to a desired channel after a predetermined number of transmissions and total reflections.
Accordingly, an optical signal can be transmitted to a channel in a desired direction by transmitting or total reflecting the optical signal. However, in the above optical switch, since the heater 115 that heats liquid is manufactured together with the cell 110 on the substrate 100 where the waveguides 103 are formed, if any of the heaters 115 do not work during the operation of the optical switch, the entire optical switch cannot be used due to that malfunctioning heater 115, which results in inefficiency and increased costs in optical manufacturing. There is another method of heating the liquid by applying a voltage thereto instead of using the heater. This method also has the same problems. Further, since the optical switch is configured in the form of an Nxc3x97M matrix, which is not a simple form, installing the waveguides, heaters, and cells together on the substrate requires a very accurate and complicated manufacturing process, thus reducing productivity.
Accordingly, it is an object of the present invention to provide an optical switch in which liquid is heated by using laser heating units that are installed in a separable manner from the substrate where waveguides are provided, so that, when any of the lasers within the laser heating units does not work, only the malfunctioning laser heating unit needs to be replaced rather than the whole optical switch.
Additional objects and advantages of the invention will be set forth in part in the description which follows and, in part, will be obvious from the description, or may be learned by practice of the invention.
The foregoing and other objects of the present invention are achieved by providing: optical switch substrates; waveguides through which an optical signal is transmitted, the waveguides being arranged in the form of a matrix between the substrates and having at least one cross point; cells, each containing liquid and arranged at each cross point of the waveguides; and a laser heating unit having lasers corresponding to the respective cells to selectively heating the liquid in each cell.
The above and other objects of the present invention may also be achieved by providing a microlens array between the cells and the lasers corresponding to each of the cells so that light emitted from each of the lasers is focused on each cell.
The above and other objects of the present invention may be achieved by providing that the laser heating unit is installed to be detachable from the substrates.